TIL: PHP IIS 8kb Request Limit?

TIL: PHP IIS 8kb Request Limit? Today, at $dayjob, I was called into a remote debugging session. For some reason the DokuWiki install at a customer failed to save long pages. Instead of saving, the editor just reloaded and showed the previous state again. No errors in DokuWiki and none to be found in the various places PHP and the web server used for logging. Now this was on a Windows machine with IIS as the web server using PHP via CGI. Not my recommended setup but somewhat common in business contexts. The weird thing was, when the customer switched back to an older release of PHP it worked again. I created a simple test script to make sure it was not DokuWiki's fault and sure enough: the same issue there. Posting a “hello” worked, posting a 50kb test text resulted in a zero byte request body. Using another quick script, we found out that the exact limit was 8192 bytes - 8kB. I checked all the usual suspects: post size, any kind of limit in IIS. Nothing. I had to leave the session…